The present invention relates to a PHS data communication terminal adapter, and in particular, to a PHS data communication terminal adapter which performs data communication with a data communication terminal on the side of a PHS (Personal Handy-phone System) via a digital network by executing protocol conversion and switching the data transmission bit rate between a high data transmission bit rate and a low data transmission bit rate.
In Personal Handy-phone System (PHS) which has been developed in Japan, data communication terminals which can be connected to PHS handy phones are widely used in order to communicate data, and PHS data communication terminals having radio transmission/reception capability are also utilized. Therefore, communication of data can be executed between data communication terminals which are connected to PHS handy phones, between a PHS data communication terminal (having radio transmission/reception capability) and a data communication terminal which is connected to a PHS handy phone, or between PHS data communication terminals (having radio transmission/reception capability). In the data communication in the PHS, data is transmitted mainly at a bit rate of 32 kbps based on CCITT-I430, and a data transmission bit rate of 64 kbps is also utilized. In Japan, the Personal Handy-phone System is connected with ISDN (Integrated Services Digital Network) and PSTN (Public Switched Telephone Network), and thus data communication between a data communication terminal which is connected to a PHS handy phone (or a PHS data communication terminal having radio transmission/reception capability) and a data communication terminal on the side of the ISDN or PSTN is also possible.
With regard to the Personal Handy-phone System, proposals for standardization of data transmission protocols etc. have been done in order to make data transmission and access to Internet using PHS handy phone easier, in which xe2x80x9cPIAFSxe2x80x9d (PHS Internet Access Forum Standard) has been standardized in March 1997 by PHS Internet Access Forum (JAPAN). In the PIAFS, methods for controlling synchronized systems in PIAFS data transmission protocol conversion, full-duplex data communication, measurement of answer delay time, flow control, data link establishment/release, data assembing(framing)/disassembling functions, data compression function, etc. have been standardized. Frame types such as negotiation frames, synchronization frames, control frames, data frames, etc. have also been standardized.
As mentioned above, when a data communication terminal on the side of an Integrated Services Digital Network (ISDN) communicates with a data communication terminal on the side of a Personal Handy-phone System (PHS) via the ISDN, data communication is executed at a data transmission bit rate of 32 kbps or 64 kbps in information channels (2Bch) according to the CCITT-1430. The 64 kbps data transmission bit rate is utilized when radio wave conditions for the PHS handy phone are good, and the data transmission bit rate is switched to 32 kbps if the radio wave conditions are not good. The switching of the data transmission bit rate between 32 kbps and 64 kbps is determined and executed exclusively by the data communication terminal on the side of the PHS, since the radio wave conditions are detected on the side of the PHS.
Data transmission from a data communication terminal on the side of a PHS network to a data communication terminal (such as a personal computer) on the side of an ISDN is executed, for example, via a PHS handy phone, a radio base station of the PHS network, the PHS network, the ISDN, an NCU (Network Control Unit), and a PHS data communication terminal adapter to which the data communication terminal on the side of the ISDN is connected. Data transmission from the data communication terminal on the side of the ISDN to the data communication terminal on the side of the PHS network is executed reversely.
Data communication between a PHS handy phone (to which the data communication terminal on the side of the PHS is connected) and the PHS network is executed using (2Bxe2x80x2+D) channels. The data transmission bit rate of the Bxe2x80x2-channel is 32 kbps or 64 kbps as mentioned above, and the data transmission bit rate of the D-channel is 16 kbps.
The ISDN communicates data utilizing (2B+D) channels (2xc3x97 (32 kbps or 64 kbps)+16 kbps). Here, in the ISDN, the basic data transmission bit rate is fixed to 64 kbps, in which 8-bit B-channel transmission data is transmitted at a frequency of 8 kHz (8 bitsxc3x978 kHz). Therefore, the 32 kbps (4 bitsxc3x978 kHz) B-channel transmission data of the ISDN is transmitted utilizing front 4 bits of the 8-bit B-channel transmission data, and rear 4 bits of the 8-bit B-channel transmission data is filled with dummy data such as xe2x80x9c1111xe2x80x9d.
When the 32 kbps Bxe2x80x2-channel data is sent from the PHS handy a phone, an exchange (switch) of the PHS network converts the 32 kbps Bxe2x80x2-channel data to the 32 kbps B-channel transmission data (in which the front 4 bits of the 8-bit B-channel transmission data are utilized and the rear 4 bits of the 8-bit B-channel transmission data are filled with the dummy data), and sends the 32 kbps B-channel transmission data to the ISDN.
The PHS data communication terminal adapter (TAP) (to which the data communication terminal on the side of the ISDN is connected) which communicates data with the data communication terminal on the side of the PHS network via the ISDN utilizing data transmission bit rates of 32 kbps and 64 kbps operates as follows.
(1) When the PHS data communication terminal adapter is in a SETUP status (when the PHS data communication terminal adapter and the data communication terminal on the side of the PHS have just been established connection, by communicating control information using setup signals on the D-channel), the data communication terminal on the side of the PHS which is going to transmit data to the PHS data communication terminal adapter on the side of the ISDN can not inform the PHS data communication terminal adapter whether its data transmission bit rate is 32 kbps or 64 kbps. Therefore, the data-receiving PHS data communication terminal adapter on the side of the ISDN has to execute the following PIAFS protocol conversions at once or successively, in order to judge whether the data transmission bit rate of the datasending data communication terminal on the side of the PHS is 32 kbps or 64 kbps and set protocol conversion mode of itself at a xe2x80x9chigh rate protocol conversion modexe2x80x9d which corresponds to the high data transmission bit rate (64 kbps) or a xe2x80x9clow rate protocol conversion modexe2x80x9d which corresponds to the low data transmission bit rate (32 kbps) based on the judgment.
(a) The PHS data communication terminal adapter executes 64 kbps PIAFS protocol conversion to all the bits of the 64 kbps B-channel transmission data.
(b) The PHS data communication terminal adapter executes 32 kbps PIAFS protocol conversion to the front 4-bit data of the 64 kbps B-channel transmission data composed of 8 bits.
(2) When data transmission bit rate is changed from 64 kbps to 32 kbps by the data communication terminal on the side of the PHS by channel switching during data communication, the PHS data communication terminal adapter has to execute the following PIAFS protocol conversions at once or successively, in order to judge whether the data transmission bit rate of the data-sending data communication terminal on the side of the PHS is 32 kbps or 64 kbps and set the protocol conversion mode of itself at the high rate protocol conversion mode corresponding to the high data transmission bit rate (64 kbps) or the low rate protocol conversion mode corresponding to the low data transmission bit rate (32 kbps) based on the judgment.
(a) The PHS data communication terminal adapter executes 32 kbps PIAFS protocol conversion to the front 4-bit data of the 64 kbps B-channel transmission data composed of 8 bits.
(b) The PHS data communication terminal adapter executes 32 kbps PIAFS protocol conversion to the rear 4-bit data of the 64 kbps B-channel transmission data composed of 8 bits.
(c) The PHS data communication terminal adapter executes 64 kbps PIAFS protocol conversion to all the bits of the 64 kbps B-channel transmission data.
(3) On the other hand, when data transmission bit rate is changed from 32 kbps to 64 kbps by the data communication terminal on the side of the PHS by channel switching during data communication, the PHS data communication terminal adapter has to execute the above three PIAFS protocol conversions ((a), (b) and (c)) at once or successively, in the same way as the above case.
In the PHS data communication terminal adapter, when the data transmission bit rate is switched between 32 kbps and 64 kbps, CRC (Cyclic Redundancy Check) error might occur frequently in the SETUP status or during data transmission. In such cases, synchronization has to be established again, and thus the above PIAFS protocol conversions (a), (b) and (c) in (2) and (3) have to be executed at once or successively. In order to execute the three PIAFS protocol conversions (a), (b) and (c) at once (simultaneously), such a PHS data communication terminal adapter (employing the PIAFS protocol conversion and performing data communication with a data communication terminal on the side of the PHS via the ISDN switching the data transmission bit rate between 32 kbps and 64 kbps) has to be provided with three PIAFS protocol conversion sections.
As described above, when the PIAF standard is employed and data communication is executed via the ISDN switching the data transmission bit rate between 32 kbps and 64 kbps, three PIAFS protocol conversions have to be executed by the PHS data communication terminal adapter at once or successively. In order to execute the three PIAFS protocol conversions at once, the PHS data communication terminal adapter has to be provided with three PIAFS protocol conversion sections. On the other hand, in the case where the three PIAFS protocol conversions are executed successively, long time has to be spent in order to establish synchronization again. As a result, signal processing scale and device scale of the PHS data communication terminal adapter have to be large or data communication efficiency has to be deteriorated, in order to perform data communication via the ISDN employing the PIAFS protocol conversion and switching the data transmission bit rate between 32 kbps and 64 kbps.
While cases in Japan have been described above, similar type of data communication between data communication terminals is also done popularly in the U.S.A. etc. For example, many buildings are provided with private digital networks according to ISDN to which a plurality of data communication terminals (such as personal computers) are connected, and a plurality of PHS handy phones can be connected with the private digital network via radio waves. In such cases, a PHS handy phone is connected to the private digital network via a PBX (Private Branch Exchange) of the private digital network. Data transmission from a data communication terminal which is connected to the PHS handy phone to a data communication terminal (such as a personal computer) on the side of the private digital network is executed, for example, via the PHS handy phone, a PBX of the private digital network, the private digital network, and a PHS data communication terminal adapter to which the data communication terminal on the side of the private digital network is connected. Data transmission from the data communication terminal on the side of the private digital network to the data communication terminal on the side of the PHS handy phone is executed reversely.
Data communication between a PHS handy phone (to which the data communication terminal on the side of the PHS handy phone is connected) and a PBX of the private digital network is executed using (2Bxe2x80x2+D) channels. The data transmission bit rate of the Bxe2x80x2-channel is 32 kbps or 64 kbps, and the data transmission bit rate of the D-channel is 16 kbps.
The private digital network communicates data utilizing (2B+D) channels (2xc3x97(32 kbps or 64 kbps)+16 kbps) according to the ISDN. Therefore, also in the private digital network, the basic data transmission bit rate is fixed to 64 kbps, and 8-bit B-channel transmission data is transmitted at a frequency of 8 kHz (8 bitsxc3x978 kHz). Thus, the 32 kbps (4 bitsxc3x978 kHz) B-channel transmission data of the private digital network is transmitted utilizing front 4 bits of the 8-bit B-channel transmission data, and rear 4 bits of the 8-bit B-channel transmission data is filled with dummy data such as xe2x80x9c1111xe2x80x9d.
When the 32 kbps Bxe2x80x2-channel data is sent from the PHS handy phone, a PBX of the private digital network converts the 32 kbps Bxe2x80x2-channel data to 32 kbps B-channel transmission data (in which the front 4 bits of the 8-bit B-channel transmission data are utilized and the rear 4 bits of the 8-bit B-channel transmission data are filled with the dummy data), and transmits the 32 kbps B-channel transmission data in the private digital network.
The 64 kbps data transmission bit rate is utilized when radio wave conditions for the PHS handy phone are good, and the 32 kbps data transmission bit rate is utilized when radio wave conditions for the PHS handy phone are not good. The switching of the data transmission bit rate between 32 kbps and 64 kbps is determined and executed exclusively by the data communication terminal on the side of the PHS handy phone, since the radio wave conditions are detected on the side of the PHS handy phone.
Similarly to the aforementioned cases of JAPAN, the PHS data communication terminal adapter (to which the data communication terminal on the side of the private digital network is connected) which communicates data with the data communication terminal on the side of the PHS handy phone via the private digital network utilizing data transmission bit rates of 32 kbps and 64 kbps also has to execute the aforementioned three PIAFS protocol conversions ((a), (b) and (c)) at once or successively, in order to judge whether the data transmission bit rate of the data-sending data communication terminal on the side of the PHS handy phone is 32 kbps or 64 kbps and set the protocol conversion mode of itself at the high rate protocol conversion mode corresponding to the high data transmission bit rate (64 kbps) or the low rate protocol conversion mode corresponding to the low data transmission bit rate (32 kbps) based on the judgment. Therefore, also in the case of the U.S.A. etc., such a PHS data communication terminal adapter (employing the PIAFS protocol conversion and performing data communication with a data communication terminal on the side of the PHS handy phone via the private digital network switching the data transmission bit rate between 32 kbps and 64 kbps) has to be provided with three PIAFS protocol conversion sections, in order to execute the three PIAFS protocol conversions (a), (b) and (c) simultaneously. In the case where the three PIAFS protocol conversions are executed successively, long time has to be spent in order to establish synchronization again. Therefore, similarly to the case of Japan, signal processing scale and device scale of the PHS data communication terminal adapter have to be large or data communication efficiency has to be deteriorated in order to perform data communication via the private digital network employing the PIAFS protocol conversion and switching the data transmission bit rate between 32 kbps and 64 kbps.
Incidentally, the problems mentioned above exist also when protocol conversion other than PIAFS protocol conversion is employed by the PHS data communication terminal adapter.
It is therefore the primary object of the present invention to provide a PHS data communication terminal adapter which can perform data communication with a data communication terminal on the side of a PHS (Personal Handy-phone System) via a digital network by executing protocol conversion and switching the data transmission bit rate between a high data transmission bit rate and a low data transmission bit rate, without needing large signal processing scale and device scale, and without deteriorating data communication efficiency.
In accordance with a first aspect of the present invention, there is provided a PHS data communication terminal adapter which is provided as a terminal adapter of a first data communication terminal to a digital network for performing data communication with a second data communication terminal on the side of a PHS via the digital network by executing protocol conversion, comprising a protocol conversion means, a data transmission bit rate judgment means, and a protocol conversion mode setting means. The protocol conversion means executes protocol conversions which are needed for data communication between the first data communication terminal and the second data communication terminal on the side of the PHS via the digital network. The data transmission bit rate judgment means judges whether the data transmission bit rate of B-channel transmission data which is supplied from the second data communication terminal via the digital network is a high data transmission bit rate corresponding to the basic rate of the digital network or a low data transmission bit rate corresponding to xc2xd of the basic rate of the digital network, utilizing a frame synchronizing signal, transmission data and a basic rate clock signal concerning the B-channel transmission data. And the protocol conversion mode setting means sets the protocol conversion mode of the protocol conversion means at a high rate protocol conversion mode corresponding to the high data transmission bit rate or a low rate protocol conversion mode corresponding to the low data transmission bit rate, based on the judgment executed by the data transmission bit rate judgment means.
In accordance with a second aspect of the present invention, in the first aspect, the data transmission bit rate judgment means includes a digital network interface section, a bit separation section, a counter section, and a judgment section. The digital network interface section operates as the interface of the PHS data communication terminal adapter to the digital network. The bit separation section separates the front 4-bit data or the rear 4-bit data of 8-bit B-channel transmission data which is supplied from the digital network interface section utilizing the frame synchronizing signal and the basic rate clock signal. The counter section counts the number of xe2x80x9c1xe2x80x9ds or xe2x80x9c0xe2x80x9ds in the front 4-bit data or the rear 4-bit data which has been separated by the bit separation section. And the judgment section judges whether the data transmission bit rate of the B-channel transmission data is the high data transmission bit rate or the low data transmission bit rate based on the number of xe2x80x9c1xe2x80x9ds or xe2x80x9c0xe2x80x9ds which has been counted by the counter section.
In accordance with a third aspect of the present invention, in the second aspect, the bit separation section includes a counter and an AND gate. The counter is reset by the frame synchronizing signal which is supplied from the digital network interface section, counts edges of the basic rate clock signal which is supplied from the digital network interface section, and outputs a gate signal which includes a High/Low-level front part corresponding to four pulses of the basic rate clock signal and a Low/High-level rear part corresponding to four pulses of the basic rate clock signal. The AND gate is supplied with the B-channel transmission data and the gate signal which has been non-inverted/inverted, thereby the AND gate obtains the front 4-bit data of the 8-bit B-channel transmission data and supplies the front 4-bit data to the counter section.
In accordance with a fourth aspect of the present invention, in the second aspect, the bit separation section includes a counter and an AND gate. The counter is reset by the frame synchronizing signal which is supplied from the digital network interface section, counts edges of the basic rate clock signal which is supplied from the digital network interface section, and outputs a gate signal which includes a High/Low-level front part corresponding to four pulses of the basic rate clock signal and a Low/High-level rear part corresponding to four pulses of the basic rate clock signal. The AND gate is supplied with the B-channel transmission data and the gate signal which has been inverted/non-inverted, thereby the AND gate obtains the rear 4-bit data of the 8-bit B-channel transmission data and supplies the rear 4-bit data to the counter section.
In accordance with a fifth aspect of the present invention, in the first aspect, the digital network is a narrow-band ISDN (Integrated Services Digital Network), in which the high data transmission bit rate is 64 kbps and the low data transmission bit rate is 32 kbps.
In accordance with a sixth aspect of the present invention, in the first aspect, the digital network is a private digital network according to the narrow-band ISDN (Integrated Services Digital Network), in which the high data transmission bit rate is 64 kbps and the low data transmission bit rate is 32 kbps.
In accordance with a seventh aspect of the present invention, in the first aspect, the protocol conversion means executes protocol conversion according to PIAFS (PHS Internet Access Forum Standard).